1. Field of the Invention
The present invention relates to a heart stimulating device having the capability for measurement and qualification of the degree of congestive heart failure. The determined congestive heart failure indicator value—alone or together with other metrics—may advantageously be use in assessing the patient's status, titrating drugs and/or evaluating therapy.
2. Description of the Prior Art
Approximately 23 million people worldwide are afflicted with congestive heart failure (CHF), and 2 million new cases of CHF are diagnosed each year worldwide. In contrast to other cardiovascular disorders that have actually declined during the past few decades, the incidence of heart failure is one that rises. It is, in fact, the most rapidly growing cardiovascular disorder in the United States.
Congestive heart failure is a chronic inability of the heart to maintain an adequate output of blood from one or both ventricles of the heart to meet the metabolic demands of the tissues. With a markedly weakened left ventricle or right ventricle or both, the volume of blood presented to the heart is in excess of the heart's capacity to move it along. Consequently, fluid builds up behind the heart. With a weakened left ventricle or right ventricle or both, there is a shift of large volumes of blood from the systemic circulation into the pulmonary (lung) circulation. If the inability to move the volume of blood forward is due to a left heart side problem without the right side falling as well, blood continues to be pumped into the lungs by the normal right heart side, while it is not pumped adequately out of the lungs by the left heart side. As the volume of blood in the lungs increases, the pulmonary vessels enlarge, pulmonary venous congestion develops, and, once the pulmonary capillary pressure rises above a critical point, fluid begins to filter out of the capillaries into the interstitial spaces and alveoli (air sacs in the lungs where exchange of oxygen and carbon dioxide occurs), resulting in pulmonary oedema. Subsequently this can lead to pleural effusion (effusion is the escape of fluid into a part) and abdominal effusion. If the abnormality lies in the right heart side or the pulmonary arteries, limiting the ability to move blood forward, then congestion occurs behind the right heart side (causing pleural effusion and/or build up of fluid in the abdomen).
Although advances in pharmacology have led to better treatment, 50% of the patients with the most advanced stage of heart failure die within a year. Typically, heart failure patients receive several chronic oral therapies, including diuretics, ACE inhibitors, beta-blockers and inotropic agents.
A majority of patients are treated with drug therapy, but for patients with advanced CHF, device-based therapy or transplantation are their only alternatives. A large number of patients with advanced CHF have received left ventricular assist devices, and a number of promising technologies, including biventricular pacing and defibrillators, ventricular remodelling, and ventricular assist devices represent exciting, growing markets.
U.S. Pat. No. 6,821,249 relates to a temperature monitoring of congestive heart failure patients as an indicator of worsening condition by using the analysis of the speed and pattern of temperature change in a way that is individualized toward patient's health condition. Body sites to measure body temperature can be characterized as “core” or “peripheral” sites, meaning deep inside the body or near the surface, but even sites classified in that manner do not necessarily behave in the same way. Temperature sensors may be any temperature sensor known that is practically applicable, and include thermocouples, resistance temperature detectors or thermistors, thermosensitive chromophores, thermosensitive liquid crystals, infrared detectors and ultrasound detectors.
U.S. Pat. No. 6,821,249 also discusses the influence of the patient's activity that is suitably monitored by an accelerometer or a vibration sensor that provides a signal that upon conversion to digital form is usable by a microprocessor for an adjustment to a temperature attribute or to the sensitivity of detection of that attribute. The same concepts for adjusting a temperature reading or sensitivity of a cut-off point apply as for medications, including use of a learning algorithm to personalize the effect of temperature change from different levels of activity.
At the onset of physical activity, the amount of blood reaching heart from the outer extremities is increased. As the temperature of the blood in the outer extremities is lower, there is a dip in the temperature of the blood in the heart. After the dip, the temperature rises with time to a level above the initial as a cause of the activity. The maximal increase in temperature as a result of activity is approximately 1.5° C.
The temperature dip at the onset of activity is patient dependent, but especially pronounced in CHF patients. This is e.g. described in “Cardiac Pacing and ICDs”, 3rd edition, Kenneth A. Ellenbogen & Mark A. Wood, page 110.
U.S. Pat. No. 4,719,920 discloses an exercise-responsive rate-adaptive cardiac pacemaker adapted to distinguish between physiologically determined changes of the patient's blood temperature under conditions of exercise and non-exercise. The pacemaker is also capable of recognizing the blood temperature dip which is characteristic of the commencement of exercise.